InGaN-based Blue Laser Diodes Research Articles

Research on Optimization of p-Type Waveguide Layer and Active Region of InGaN-Based Blue Laser Diodes

Research on Optimization of p-Type Waveguide Layer and Active Region of InGaN-Based Blue Laser Diodes

Comparative investigation into key optoelectronic characteristics of semipolar InGaN blue laser diodes: A strategy to mitigate quantum-confine stark effect

In recent years, semipolar InGaN-based blue laser diodes (LDs) have raised indescribable appeal within solid-state lighting industry as promising alternatives for currently available polar c-plane LDs due to reduction in internal polarization field and related quantum-confined stark effect. However, any comparative study in terms of energy band gap, optical emission profile, power output (P) and forward bias response (I-V) etc. between semipolar-oriented InGaN blue LDs is inherently unattainable. This work aims to demonstrate the impact of internal polarization field on aforementioned key optoelectronic parameters of In0.17Ga0.83N/GaN double quantum well (DQW) blue LD along semipolar (101-2), (112-2), (101-1), (202-1), (303-1-), (202-1-) and (101-1-) crystal orientations by figuring out six-band k.p Hamiltonian at the brillouin zone center aided from Euler’s tensor transformation method. Three-level rate equations based LD analogous circuit model and state-space matrix are employed here to obtain P-I-V and frequency characteristics. Radiative as well as non-radiative recombination mechanisms for LD systems are portrayed by addressing modified ABC model. Our numerical investigation illustrates that best hole effective mass, optical gain, lasing power, threshold current and forward voltage can be attained from (112-2)-oriented InGaN blue LD due to insignificant presence of spontaneous plus piezoelectric (PZ) polarization charge. In addition with these, the inspection of bode plot and relevant optical power gain (dB) confirms the stability and superiority of this semipolar blue LD system for achieving high-speed visible-light communications at relatively low current densities.

Enhancing the performance of InGaN/GaN multiple quantum well blue laser diodes by suppressing the overflow of holes

Transportation of carriers in c-plane InGaN-based blue laser diodes (LDs) has been investigated by both experimental and simulation methods. It is found that excepting the leakage of electrons, holes may overflow from InGaN/GaN multiple quantum wells (MQWs) and enter into InGaN lower waveguide (LWG) layer. It leads to the increase of recombination rate in LWG layer and results in the waste of carriers. Ultimately degrades the performance of LDs. In addition, we also found that reducing the thickness of GaN first barrier (FB) layer can suppress the leakage of holes due to the decrease of the effective depth of potential well in InGaN LWG layer, a lower effective depth of potential well in InGaN LWG layer is helpful the holes coming back to well layer and therefore the threshold current decreases to 80% when the FB layer thickness decreases from 20 nm to 1 nm.

Variations in junction capacitance and doping activation associated with electrical stress of InGaN/GaN laser diodes

This paper presents a study of the effects of combined electrical and thermal stress tests on commercially-available InGaN-based blue laser diodes. By means of electrical and optical measurements, we have found that stress has two major consequences: (i) an initial decrease in threshold current, which is ascribed to the increase in the activation of p-type dopant, and (ii) a subsequent increase in threshold current, which – based on optical and electrical characterization – is ascribed to the generation/propagation of non-radiative defects within the active region of the devices.

Analysis of below-threshold efficiency characteristics of InGaN-based blue laser diodes

In this study, we investigate the below-threshold emission characteristics of InGaN-based blue laser diodes (LDs) emitting at 442 nm to study the efficiency droop effects in InGaN LDs. From the measurement of spontaneous emission in the LD, it is observed that the peak efficiency appears at a current density of ∼20 A/cm2 and the efficiency at the threshold current density of ∼2.3 kA/cm2 are reduced to ∼47% of the peak efficiency. The measured spontaneous emission characteristics are analyzed using the carrier rate equation model, and the peak internal quantum efficiency is found to be ∼75% using the fit of the measured efficiency curve. In addition, the Auger recombination coefficient of the measured InGaN blue LD is found to be 10−31–10−30 cm6/s, which is somewhat lower than that reported for InGaN-based blue light-emitting diodes. It is discussed that low dislocation density and uniform current injection in quantum wells may have resulted in the low Auger recombination coefficient of InGaN LDs.

Investigation of the radiative efficiency and threshold in InGaN laser diodes under the influence of efficiency droop

Based on the rate equation model of semiconductor lasers, the radiative efficiency and threshold current density of InGaN-based blue laser diodes (LDs) are theoretically investigated, including the effect of efficiency droop in the InGaN quantum wells. The peak point of the radiative efficiency versus current density relation is used as the parameter of the rate equation analysis. The threshold current density of InGaN blue LDs is found to depend strongly on the maximum radiative efficiency at low current density, implying that improving the maximum efficiency is important to maintain a high radiative efficiency at a large current density and to achieve a low-threshold lasing action under the influence of efficiency droop.

Improvement of hole injection and electron overflow by a tapered AlGaN electron blocking layer in InGaN-based blue laser diodes

We studied the influence of a tapered AlGaN electron blocking layer (EBL) with step-graded aluminum composition on hole injection and electron overflow effects in InGaN-based laser diodes (LDs) theoretically. Schrödinger-Poisson self-consistent method together with transfer matrix method was applied to calculate carrier distribution and transport properties for both electrons and holes in tapered EBL and conventional EBL. The results indicate that the new structure favors the tunneling of low energy holes from the p-side to the active region. Meanwhile, more uniform carrier distribution and better balance between electrons and holes are obtained for the tapered structure by proper modification of band diagrams. An advanced device simulation shows the elimination of electron overflow even at a current of 180 mA in the LD with tapered EBL. Decrease of threshold current density from 2.0 kA/cm2 to 1.6 kA/cm2 is benefited from the more uniform local gain profile.

Emission characteristics of GaN-based blue lasers including a lattice matched Al0.83In0.17N optical blocking layer for improved optical beam quality

We demonstrate room-temperature continuous-wave operation of 425 nm InGaN-based blue laser diodes including a thin Al0.83In0.17N optical blocking layer. Structures are grown on c-plane GaN freestanding substrates with a lattice-matched AlInN layer positioned below an Al0.07Ga0.93N bottom cladding. Such devices are compared to standard InGaN based lasers looking at threshold current density, electrical characteristics, and far-field emission. Threshold current densities of 4 kA/cm2 and slope efficiencies of ∼0.6 W/A (for uncoated facets) have been achieved in AlInN containing devices. Lower mode leakage in the substrate is highlighted by a better transversal far-field pattern resulting in an improved beam quality.

M -plane pure blue laser diodes with p-GaN/n-AlGaN-based asymmetric cladding and InGaN-based wave-guiding layers

Asymmetric p-GaN/n-AlGaN-cladded InGaN-based pure blue (440–460 nm) laser diodes were fabricated based on the nonpolar m-plane GaN technology. Simulation results showed high indium content (5%–10%) InGaN wave-guiding layers mainly contributed to the optical confinement, so that n-AlGan layer can be used to control of the peak position of the optical mode to achieve high optical confinement factor and low internal loss. By using this laser structure, lasing wavelengths of 443 and 465 nm with threshold current densities 14 and 19 kA/cm2, respectively, were demonstrated without facet coating.

Optical output power-dependent degradation mechanism of 445 nm InGaN blue laser

The degradation characteristics of InGaN-based blue laser diodes (LDs) are investigated at an emission wavelength of 445 nm. Two different LDs are used to determine the distinct failure characteristics with mirror reflectivities of 54% and 78%. Blue LDs are operated with the same current injection during a 1000 h reliability test. Each LD gives an output power of 100 mW and 50 mW at reflectivities of 54% and 78%, respectively. A slight threshold current increase is observed after 1000 h of aging at 50 mW, while the slope efficiency remains constant at its initial level before aging. At 100 mW, the slope efficiency (threshold current) increases 25% (100%) compared to values before aging. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cavity-length dependent thermal characteristics of InGaN blue laser diodes

Thermal characteristics of InGaN-based blue laser diodes (LDs) emitting around 450 nm are investigated with varying cavity length of the LDs. Characteristic temperature, junction temperature, and thermal resistance are measured for the cavity length from 650 to 1450 m. It is found that the characteristic temperature increases slowly with cavity length, and the thermal resistance is significantly improved from 30 W to 17 K/W as the cavity length increases length from 650 to 1450 m.

InGaN-based blue light-emitting diodes and laser diodes

InGaN single-quantum-well-structure blue light-emitting diodes (LEDs) were grown on epitaxially laterally overgrown GaN (ELOG) and sapphire substrates. The emission spectra showed a similar blueshift with increasing forward currents between both LEDs. The LED on sapphire had a considerable amount of leakage current in comparison with that on ELOG. InGaN multi-quantum-well structure laser diodes with modulation-doped strained-layer superlattice cladding layers fabricated on the ELOG substrate were demonstrated to have a lifetime of more than 8000 h.

High-power InGaN-based blue laser diodes with a long lifetime

The InGaN multi-quantum-well-structure laser diode (LD) was grown on an epitaxially laterally overgrown GaN on sapphire. The lowest threshold current densities between 1.2 and 2.8 kA/cm 2 were obtained when the number of InGaN well layer was 2. The LDs showed an output power as high as 420 mW per facet under room-temperature (RT) continuous-wave (CW) operation. The fundamental transverse mode was observed up to an output power of 100 mW. The lifetime of the LDs at a constant output power of 30 mW was 250 h under CW operation at an ambient temperature of 50°C. The longest lifetime of 4800 h at a constant output power of 2 mW under RT-CW operation was achieved.

The roles of structural imperfections in InGaN-based blue light-emitting diodes and laser diodes

REVIEW High-efficiency light-emitting diodes emitting amber, green, blue, and ultraviolet light have been obtained through the use of an InGaN active layer instead of a GaN active layer. The localized energy states caused by In composition fluctuation in the InGaN active layer are related to the high efficiency of the InGaN-based emitting devices. The blue and green InGaN quantum-well structure light-emitting diodes with luminous efficiencies of 5 and 30 lumens per watt, respectively, can be made despite the large number of threading dislocations (1 x 10(8) to 1 x 10(12) cm-2). Epitaxially laterally overgrown GaN on sapphire reduces the number of threading dislocations originating from the interface of the GaN epilayer with the sapphire substrate. InGaN multi-quantum-well structure laser diodes formed on the GaN layer above the SiO2 mask area can have a lifetime of more than 10,000 hours. Dislocations increase the threshold current density of the laser diodes.

InGaN-based blue laser diodes

The continuous-wave (CW) operation of InGaN multiquantum-well (MQW) structure laser diodes (LDs) was demonstrated at room temperature (RT) with a lifetime of 100 h. The threshold current and the voltage of the LDs were 50 mA and 5 V, respectively. The threshold current density was 8.8 kA/cm/sup 2/. The carrier lifetime and the threshold carrier density were estimated to be 3.5 ns and 1.8/spl times/10/sup 20//cm/sup 3/, respectively. The Stokes shift of the energy difference between the absorption and the emission energy of the InGaN MQW LD's were 140 meV. Both spontaneous and stimulated emission of the LD's originated from this deep localized energy state which is equivalent to a quantum dot-like state. From the measurements of gain spectra and an external differential quantum efficiency dependence on the cavity length, the differential gain coefficient, the transparent carrier density, threshold gain and internal loss were estimated to be 5.8/spl times/10/sup -17/ cm/sup 2/, 9.3/spl times/10/sup 19/ cm/sup -3/, 5200 cm/sup -1/, and 43 cm/sup -1/ respectively.